Drive dogs, what's their intended purpose?

[skunkworks]

I don't know if anyone mentioned it.... On cnc - it is also used for 'keying' the tool. Say you have a boring bar and you want to orient the spindle - move the axis over and pull it back out. (so you don't score up the finish you just machined) (or just so it goes into the tool chain correctly..

[Rich Carlstedt]

What is the purpose of the "Pin"- "Set Screw" -"Key"-"Stop"on a R* 8 Spindle ?
As I said earlier , it is not a drive key as it minimizes "freting" of the surface with repeated tool orientation
.
BUT the reason Bridgeport put it in the spindle was to act as a stop for the tool holder or collet when the tool was installed/removed--SAFELY !
Drraw-bar threads get buggered up, and so do threads in some arbors/collets with repeated use
You start the draw-bar thread in the tool which is engaged with the key, now with the right hand you can tighten the Draw-bar while the left hand engages the brake on the spindle----Done
Without a key/setscrew/stop/pin, you need to hold the tool with the left hand ( sharp edges ! ) while tightening the Draw-bar.

How this helps those who never went through Bridgeport 101 back in apprenticeship school

Rich

[Rich Carlstedt]

Do they say anything on steep tapers such as ISO 30, those are the tapers the original question was about.

Spindle Standards adopted 1943
30 Taper- 3.500 taper per foot-( 16 deg 35 ' 39.4" )
Diameter at socket gage line = 1 1/4 " -
Length= 1 7/8 "
Spindle Flange Dia= 2.7493 - 2.7488"
Pilot Dia= .692-.685"
Clearance Hole for drawbar= 21/32"
Width of Drive Key= .6255 - .6352"
Height of Drive Key= 5/16"
Distance between Drive Keys= 1.315 - 1.285"
Dia of B/C = 2.130 - 2.120"
Bolt Threads - 3/8-16 UNC-2B
Depth of Perfect Thread= 5/8"
Full Depth of Arbor Hole in Spindle = 2 7/8"
Minimum Spindle Protrusion - face to end of Column = 1/2 "
Arbor Drawbar Thread size = 1/2-13 x 3/4" UNC-3A
Arbor Thread size = 1/2-13 x 1" with 2" deep hole UNC-2B
Arbor Drive Slot Width=.630-.640 "

[DennisCA]

Do they say anything on steep tapers such as ISO 30, those are the tapers the original question was about.

[Rich Carlstedt]

Maybe this will help with some unknowns
Source
Tool Engineers Handbook - SME Book, 1943,1949,1959 Ref.
Section 100
Tapers,Spindle Noses, and Arbors
Authors from Jones and Lamson Machine tool and lead author is Director of Engineering at Brown and Sharpe
Is that enough credentials ?
Table 1 -Self HOLDING TAPERS
Lists Taper # .239 through # 1200 Total 23 variations including M T and B & S ( Jacobs and Jarno # in later Table)
"means of driving and holding "
All Listed as "Tang Drive with Shank held in by Friction"

Side note on MT tapers..Sockets have two standards for depth for same size MT one without tang and the other for tang use ..
ie MT # 2 is 2 1/2" long and with Tang slot adds 7/8"

Rich

Edit- This book is larger (1,000+ pgs) than Machinery handbook and deals with machine design elements
The same book was released by SME and ASTME
https://www.ebay.com/itm/14431270124....c101113.m2108

last edit, clarified socket depth

[eKretz]

all of this "R8 key" talk is nonsense. It's a friggin' dog point set screw or a set screw with two parallel flats ground on the nose.

Can someone provide an example of a machine in which it's not a set screw?

I have never seen a "key" in an R8 spindle. "Pin" would be more apt

The nonsense is that they ever fitted such a thing to the machine in the first place. Awful design. Should have been updated.

[psomero]

all of this "R8 key" talk is nonsense. It's a friggin' dog point set screw or a set screw with two parallel flats ground on the nose.

Can someone provide an example of a machine in which it's not a set screw?

I have never seen a "key" in an R8 spindle. "Pin" would be more apt

[psomero]

R-8 should really be used with a drive key also but they are notorious for breaking and causing all sorts of damage.

R8 drive key? huh?

[old mart]

The R8 taper is very close to the BT30, 40 and 50 taper angle. So close that I have some BT30 taper cleaners to use on the Tom Senior. The cleaner only works because the pin was never installed when I did the R8 mod, the spindle had a location hole partially drilled, but not reaching the bore. The only tooling that can slip during installation are the R8 collets which have next to nothing to hold onto. I make sure the drawbar threads have had a tap put through them and are clean and lubricated with moly grease.
I would like to have drive dogs in the R8 design, but so far with 2 mills we have never had a slippage. R8 is an old design best used on smaller home shop mills of 2hp or less. I like it for the easy changing of tools, no jamming Morse tapers and the huge variety of tooling still available.
The drive dogs on industrial mills mostly using ISO/BT40 are insurance against misshaps as dozens of toolchanges are made during many CNC operations.

[JRouche]

I saw a video recently...

So now I am wondering if that's true. I am always sceptical of opinions from a single person on the net, I try and find what the aggregate opinion is.

We all do that in one scale or another right. Just a part of every day life. Some say. JR

P.S. Your problem is fixable. JR

[MattiJ]

Also remember - mills used to/might still have have gear boxes. The K&T's low gear is 32:1... So with our measly 5hp spindle motor at 15 ft-lbs at 1800rpm - that is 480 ft-lbs at 56rpm.

50 taper holds quite a bit of torque even on its on but not 480 ft/lbs
Assuming 5000lbs drawbar force as per recommendations https://tacrockford.com/technical/ma...amping-forces/
--> 50 taper max torque is about 250 ft/lbs

Note also that Morse taper relies heavily on feed pressure to transmit torque.

[Tundra Twin Track]

Correct. The tang on those Morse taper tools that actually do have a tang only "engages" with the removal wedge, nothing else. I have cut off the tang on an MT3 drill chuck adapter so that the lathe tail stock could read "0" rather than starting at about 5/8in. All the holding on MT is provided by its shallow taper, and in fact in many cases you could shorten the taper by a fair bit and still have plenty of holding power.

Some MT with no tang are not compatible with some holders,the taper is the same but near impossible to remove after seated.My Mt 4 Skoda Live Center fits fine in a Dormer MT extension but is short not extending into the slot so no meat for drift key to contact.

[MrWhoopee]

Hey, MrWhoopee, I know that the R8 taper is close to the critical angle for self locking. I understand it was picked on purpose for that. So MOST of the time a little upward pressure would be enough to let the drawbar get a hold and set the locking pressure. But did you find that now and then one of the arbors would not self grab all that well?

Can't say that I've noticed. I make sure that the threads in the collets/tool shanks and on the drawbar turn freely enough that holding the collet or tool up whilst giving the drawbar a spin pulls it up and seats the taper nicely. Never encountered one that wouldn't. Maybe I've just been lucky.

[SVS]

Cleveland Forge 4mt 1 7/8”

Somewhere else in my collection I have a bit that I cut the tang off, seated it solidly in a 4-5mt sleeve and it’s forevermore a 5mt shank.

[eKretz]

You say the tang would twist off before the tool. The standard tang has a very generous fillet where it connects to the tapered section of the adopter. A tool mounted in a holder or collet has no such fillet so the stress at the point where it enters the holder of collet must be a high stress area. Is there any actual evidence for your statement or is it just a wag (wild ass guess)?

Experience dictates just about all of my responses. I have seen it many times.